Warped Passages Read Free Page B

more remarkable. Although physicists have assumed for eighty years that extra dimensions must be tiny in order to explain why we haven’t seen them, in 1999 Raman and I discovered that not only can warped space explain gravity’s feebleness,but also that an invisible extra dimension can stretch out to infinity, provided it is suitably distorted in a curved spacetime. An extra dimension can be infinite in size–but nonetheless be hidden. (Not all physicists immediately accepted our proposal. But my non-physicist friends were more quickly convinced I was on to something—not because they fully grasped the physics, but because when I attended a conference banquet after speaking about my work, Stephen Hawking saved me a seat.)
    I will explain the physical principles underlying these and other theoretical developments and the new notions about space that make them conceivable. And later on, we’ll also encounter an even weirder possibility, which the physicist Andreas Karch and I discovered a year later: we could be living in a three-dimensional pocket of space, even though the rest of the universe behaves as if it is higher-dimensional. This result opens a host of new possibilities for the fabric of spacetime, which could consist of distinct regions, each appearing to contain a different number of dimensions. Not only are we not in the center of the universe, as Copernicus shocked the world by suggesting five hundred years ago, but we just might be living in an isolated neighborhood with three spatial dimensions that’s part of a higher-dimensional cosmos.
    The newly-studied membrane-like objects called branes are important components of the rich higher-dimensional landscapes. If extra dimensions are a physicist’s playground, then braneworlds —hypothesized universes in which we live on a brane—are the tantalizing, multi-layered, multi-faceted jungle gyms. * This book will take you to braneworlds and universes with curled-up, warped, large, and infinite dimensions, some of which contain a single brane and others of which have multiple branes housing unseen worlds. All of these are within the realm of possibility.
    The Excitement of the Unknown
    The postulated braneworlds are a theoretical leap of faith, and the ideas they contain are speculative. However, as with the stock market, riskier ventures might fail but they could also reward you with greater returns.

    Imagine the sight of the snow under a ski chairlift on the first sunny day after a storm, when untracked powder tempts you from below. You know that no matter what, once you hit the snow, it’s going to be a great day. Some runs will be steep and full of bumps, some will be easy cruisers, and some will be tricky routes through trees. But even if you take the occasional wrong turn, most of the day will be wonderfully rewarding.
    For me, model building—which is what physicists call the search for theories that might underlie current observations—has this same irresistible appeal. Model building is adventure travel through concepts and ideas. Sometimes new ideas are obvious, and sometimes they are tricky to find and negotiate. However, even when we don’t know where they’re heading, interesting new models often explore untouched, delightful terrain.
    We will not know right away which of the theories gets it right about our place in the universe. For some of them, we might never know. But, incredibly, that is not true for all extra-dimensional theories. The most exciting feature of any extra-dimensional theory that explains the weakness of gravity is that if it is correct, we will soon find out. Experiments that study very energetic particles could discover evidence supporting these proposals and the extra dimensions they contain within the next five years—as soon as the Large Hadron Collider (LHC), a very high energy particle collider near Geneva, is up and running.
    This collider, which turns on in 2007, will bang together tremendously energetic